/* ----------------------------------------------------------------------
 * Project:      CMSIS DSP Library
 * Title:        arm_logsumexp_f32.c
 * Description:  LogSumExp
 *
 *
 * Target Processor: Cortex-M and Cortex-A cores
 * -------------------------------------------------------------------- */
/*
 * Copyright (C) 2010-2019 ARM Limited or its affiliates. All rights reserved.
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed under the Apache License, Version 2.0 (the License); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an AS IS BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "arm_math.h"
#include <limits.h>
#include <math.h>


/**
 * @addtogroup groupStats
 * @{
 */


/**
 * @brief Computation of the LogSumExp
 *
 * In probabilistic computations, the dynamic of the probability values can be very
 * wide because they come from gaussian functions.
 * To avoid underflow and overflow issues, the values are represented by their log.
 * In this representation, multiplying the original exp values is easy : their logs are added.
 * But adding the original exp values is requiring some special handling and it is the
 * goal of the LogSumExp function.
 *
 * If the values are x1...xn, the function is computing:
 *
 * ln(exp(x1) + ... + exp(xn)) and the computation is done in such a way that
 * rounding issues are minimised.
 *
 * The max xm of the values is extracted and the function is computing:
 * xm + ln(exp(x1 - xm) + ... + exp(xn - xm))
 *
 * @param[in]  *in         Pointer to an array of input values.
 * @param[in]  blockSize   Number of samples in the input array.
 * @return LogSumExp
 *
 */

#if defined(ARM_MATH_MVEF) && !defined(ARM_MATH_AUTOVECTORIZE)

#include "arm_helium_utils.h"
#include "arm_vec_math.h"

float32_t arm_logsumexp_f32(const float32_t *in, uint32_t blockSize)
{
	float32_t       maxVal;
	const float32_t *pIn;
	int32_t         blkCnt;
	float32_t       accum = 0.0f;
	float32_t       tmp;


	arm_max_no_idx_f32((float32_t *) in, blockSize, &maxVal);


	blkCnt = blockSize;
	pIn = in;


	f32x4_t         vSum = vdupq_n_f32(0.0f);
	blkCnt = blockSize >> 2;
	while (blkCnt > 0) {
		f32x4_t         vecIn = vld1q(pIn);
		f32x4_t         vecExp;

		vecExp = vexpq_f32(vsubq_n_f32(vecIn, maxVal));

		vSum = vaddq_f32(vSum, vecExp);

		/*
		 * Decrement the blockSize loop counter
		 * Advance vector source and destination pointers
		 */
		pIn += 4;
		blkCnt --;
	}

	/* sum + log */
	accum = vecAddAcrossF32Mve(vSum);

	blkCnt = blockSize & 0x3;
	while (blkCnt > 0) {
		tmp = *pIn++;
		accum += expf(tmp - maxVal);
		blkCnt--;

	}

	accum = maxVal + log(accum);

	return (accum);
}

#else
#if defined(ARM_MATH_NEON) && !defined(ARM_MATH_AUTOVECTORIZE)

#include "NEMath.h"
float32_t arm_logsumexp_f32(const float32_t *in, uint32_t blockSize)
{
	float32_t maxVal;
	float32_t tmp;
	float32x4_t tmpV, tmpVb;
	float32x4_t maxValV;
	uint32x4_t idxV;
	float32x4_t accumV;
	float32x2_t accumV2;

	const float32_t *pIn;
	uint32_t blkCnt;
	float32_t accum;

	pIn = in;

	blkCnt = blockSize;

	if (blockSize <= 3) {
		maxVal = *pIn++;
		blkCnt--;

		while (blkCnt > 0) {
			tmp = *pIn++;

			if (tmp > maxVal) {
				maxVal = tmp;
			}
			blkCnt--;
		}
	} else {
		maxValV = vld1q_f32(pIn);
		pIn += 4;
		blkCnt = (blockSize - 4) >> 2;

		while (blkCnt > 0) {
			tmpVb = vld1q_f32(pIn);
			pIn += 4;

			idxV = vcgtq_f32(tmpVb, maxValV);
			maxValV = vbslq_f32(idxV, tmpVb, maxValV);

			blkCnt--;
		}

		accumV2 = vpmax_f32(vget_low_f32(maxValV), vget_high_f32(maxValV));
		accumV2 = vpmax_f32(accumV2, accumV2);
		maxVal = vget_lane_f32(accumV2, 0) ;

		blkCnt = (blockSize - 4) & 3;

		while (blkCnt > 0) {
			tmp = *pIn++;

			if (tmp > maxVal) {
				maxVal = tmp;
			}
			blkCnt--;
		}

	}



	maxValV = vdupq_n_f32(maxVal);
	pIn = in;
	accum = 0;
	accumV = vdupq_n_f32(0.0f);

	blkCnt = blockSize >> 2;

	while (blkCnt > 0) {
		tmpV = vld1q_f32(pIn);
		pIn += 4;
		tmpV = vsubq_f32(tmpV, maxValV);
		tmpV = vexpq_f32(tmpV);
		accumV = vaddq_f32(accumV, tmpV);

		blkCnt--;

	}
	accumV2 = vpadd_f32(vget_low_f32(accumV), vget_high_f32(accumV));
	accum = vget_lane_f32(accumV2, 0) + vget_lane_f32(accumV2, 1);

	blkCnt = blockSize & 0x3;
	while (blkCnt > 0) {
		tmp = *pIn++;
		accum += expf(tmp - maxVal);
		blkCnt--;

	}

	accum = maxVal + logf(accum);

	return (accum);
}
#else
float32_t arm_logsumexp_f32(const float32_t *in, uint32_t blockSize)
{
	float32_t maxVal;
	float32_t tmp;
	const float32_t *pIn;
	uint32_t blkCnt;
	float32_t accum;

	pIn = in;
	blkCnt = blockSize;

	maxVal = *pIn++;
	blkCnt--;

	while (blkCnt > 0) {
		tmp = *pIn++;

		if (tmp > maxVal) {
			maxVal = tmp;
		}
		blkCnt--;

	}

	blkCnt = blockSize;
	pIn = in;
	accum = 0;
	while (blkCnt > 0) {
		tmp = *pIn++;
		accum += expf(tmp - maxVal);
		blkCnt--;

	}
	accum = maxVal + logf(accum);

	return (accum);
}
#endif
#endif /* defined(ARM_MATH_MVEF) && !defined(ARM_MATH_AUTOVECTORIZE) */

/**
 * @} end of groupStats group
 */
